The baking powder is quite high and there aren't enough reviews to see if it comes out okay. You might try messaging the author before you bake it. I wouldn't substitute buttermilk, because you will likely need to reduce the baking powder and use some baking soda. The acidity throws the leavening off.

I agree that the ratio of baking powder is very high, and wonder if it might be a typo. At the very least, the measurement is odd; if correct, 8 teaspoons would equal 2 tablespoons plus 2 teaspoons. 1 to 2 teaspoons of baking powder per cup of flour is the average. You can certainly sub buttermilk. I always use buttermilk in cornbread. Since it is acidic, simply add 1/2 teaspoon for every 8 ounces of acidic ingredient. Here, 1.5 cups of buttermilk subbed for the milk would require adding 3/4 teaspoon of baking soda. Simply sift it in with the other dry ingredients. And in the absence of other information, start by halving the baking powder.

I'm so sorry; today held way too many hours at work. To clarify: If substituting buttermilk for milk in anything, add 1/2 teaspoon of baking soda for every 8 ounces of buttermilk (acidic ingredient) because buttermilk is acidic. You need the baking soda to neutralize the acid in buttermilk. If you don't add it, a portion of the baking soda present in the baking powder (baking powder contains baking soda) will be siphoned off and ultimately reduce the leavening power of baking powder alone. That's the short answer. And I hope it helps you.